1. Field of the Invention
The principal utility of the invention is with valve and actuator applications where extremely fast response is very desirable. For example, a piston engine that needs to introduce fuel through direct injection within 30 degrees of crank rotation and that is running at 4000 rpm, has 1.25 milliseconds to open the fuel injection valve, inject the fuel and close the valve. The most apparent field of application is in internal-combustion engines for motor vehicles.
2. Description of the Prior Art
The growing utilization of automobiles has greatly added to the atmospheric concentration of various pollutants including oxides of nitrogen and greenhouse gases such as carbon dioxide. In a quest for approaches which could significantly improve the efficiency of fuel utilization for automotive powertrains, while still achieving low levels of NOx emissions, the need for fast valves and actuators became apparent and this invention was conceived.
Conventional "fast" valves begin a valving change from either an open or closed position. In the closed position the "movable component" of the valve has "sealed" (usually against a seat or, in a spool valve, by positioning the spool so that flow from the high pressure port is blocked). A command to open results in a force being applied to the movable component, and movement (i.e., acceleration) of the mass of the movable component begins according to the following equation: ##EQU1##
Where:
"F" is the force applied to the movable component PA1 "M" is the mass of the movable component PA1 "a" is the acceleration of the movable component that results
The time required to move the movable component from the closed position to the fully open position is the time needed for valve opening, and this time is dependent on the acceleration and the distance the movable component must cover from the closed position to the fully open position. Conventional "fast" valves maximize acceleration by applying a very large force, minimize the mass of the movable components and minimize the travel distance by valve design to the extent possible. Extremely fast valve action (e.g., less than 1 millisecond) is therefore very difficult to achieve with conventional designs. Conventional valve designs begin the opening stage with an initial speed of zero. The acceleration rate results in a maximum speed that occurs at the end of the opening process. The average speed is therefore determined by the initial speed (i.e., zero) and the final speed, and for a near constant acceleration rate the average speed is about one half the final speed. Since the time for opening a conventional valve is the distance needed for travel to fully open the flow ports divided by the average speed, starting the valve opening from zero speed severely constrains the ability to obtain very fast valve openings.
In a conventional spool valve the "OFF" position has the spool valve port slightly withdrawn from communication with the passage through the valve body in order to provide a seal against leakage. See, for example, U.S. Pat. No. 4,770,389 issued to Bodine. This conventional sealing distance is not intended to allow the valve spool to accelerate prior to starting to open and, in fact, acceleration through a sealing zone in a conventional valve is de minimus, i.e., to less than 10% of maximum spool velocity.
In some modern "fast acting valves", the leading edge of the valve port and that of the valve body passage are "line-on-line" in the OFF position. In other words, the leading edges of the two ports are radially aligned with no sealing distance therebetween. In such valves some small amount of leakage is tolerated in order to provide a faster acting valve.